Device for forming polygonal voids in concrete members

ABSTRACT

A device for forming polygonal voids in concrete members, such as concrete beams, slabs and the like, includes an elongated, hollow, tubular body formed of a fabric reinforced, elastomeric material. The body maintains a cloverleaf or cross shape having a first predetermined, cross-sectional area when unpressurized and inflates to and maintains, without the necessity for any additional support, a square, rectangular or other polygonal shape having a second cross-sectional area greater than the first cross-sectional area. The device includes a novel end portion configuration that utilizes the tensile strength of the fabric reinforced, elastomeric, tubular body to integrally remove the end portion and the tubular body from a polygonal void formed in a concrete member.

Herro 4 1 Jan. 28, 1975 DEVICE FOR FORMING POLYGONAL VOIDS IN CONCRETEMEMBERS [75] Inventor: Richard E. Herro, Joliet, 111.

[73] Assignee: Dearborn Rubber Corporation,

Broadview, Ill.

[22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,007

Primary E.\amim'rC. W Lanham Assislun! Examiner-D. C. Reiley. lll

Attorney, Agent. or Firm-Mason, Kolehmaincn. Rathburn & Wyss [57]ABSTRACT A device for forming polygonal voids in concrete members, suchas concrete beams, slabs and the like, includes an elongated, hollow,tubular body formed of a fabric reinforced, elastomeric material, Thebody maintains a cloverleaf or cross shape having a first predetermined,cross-sectional area when unpressurized and inflates to and maintains,without the necessity for any additional support, a square, rectangularor other polygonal shape having a second crossscctional area greaterthan the first cross-sectional area. The device includes a novel endportion configuration that utilizes the tensile strength of the fabricreinforced, elastomeric, tubular body to integrally remove the endportion and the tubular body from a polygonal void formed in a concretemember.

8 Claims, Drawing Figures DEVICE FOR FORMING POLYGONAL VOIDS IN CONCRETEMEMBERS BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to devices, commonly known as cores, for usein the casting of hollow concrete members, such as beams, slabs and thelike, and, more particularly, to improved cores for forming generallysquare, rectangular and other polygonal voids in concrete members.

2. Description of the Prior Art In the manufacture of prestressedconcrete, it is a common practice to cast a concrete member, such as aconcrete beam, slab and the like, with a longitudinal opening or voidextending through its length. In the past, such a void has been formedby using a core that is expanded or pressurized while the concrete issetting and contracted or depressurized and removed from the concretethereafter.

One widely used core includes an elongated, circular, cylindrical tubehaving a wall formed of a flexible, elastomeric material, such asrubber. The tube is placed within a mold for a concrete member and thetube is enveloped with concrete when the mold is filled. The tube ispressurized and assumes and maintains a circular, cross-sectional shapewhile the concrete sets. When the concrete has set sufficiently toretain its shape. the tube is deflated and removed from the concrete.This type of core has the important advantages of simplicity and lowcost.

It has been proposed to use a core having a square, rectangular or otherpolygonal, cross-sectional shape rather than one having a circular,cross-sectional shape. A square configuration, for example, provides asavings in material cost by reducing the amount of concrete used in aconcrete member while not reducing the strength of the finished member.

It has not been found possible in the prior art to use a simple squaretube formed of an elastomeric material and constructed along the linesof the commonly used round tubes since, when pressurized, such a squaretube has consistently been found to assume a rounded or circular shape.Because of this difficulty, square cores developed by the prior art havebeen subject to the disadvantages of complexity and high cost due to thenecessity for external or metallic reinforcing structures to insure thatthe desired square shape is obtained when the core is pressurized.

In U.S. Pat. No. 3,550,897 there are disclosed structures for producingsquare voids without extraneous reinforcing structures. Thesestructures, however, have been found to suffer from disadvantages suchas expense and weight of the materials used.

SUMMARY OF THE INVENTION Accordingly, one object of the presentinvention is to provide an improved core for use in casting hollowconcrete members.

Another object of the present invention is to provide an improved coreof a very simple construction, using economical materials not havingexcessive weight, yet capable of maintaining a square shape whenpressurized.

A further object of the present invention is to provide An improved corecapable of maintaining a square shape when pressurized without thenecessity of external or metallic supporting or reinforcing structures.

In brief, the above and other objects of the present invention areachieved by providing a core for use in casting hollow concrete beams orthe like including an elongated, hollow, inflatable core body extendingbetween a pair of sealing end portions. The inflatable body includesinner and outer elastomeric sheets separated by a double layer offabric. The double layer of fabric is preferably separated by a centralsheet of elastomeric material. One or both end portions include meansfor pressurizing the inflatable body. In its unpressurized condition,the body maintains a cloverleaf or cross shape having a firstcross-sectional area. In its pressurized condition, the body inflates toform a square, rectangular or other polygonal shape having a secondcross-sectional area greater than the first crosssectional area. In itspressurized condition, the body is capable of maintaining the square,rectangular or other polygonal shape without the necessity for anyadditional support.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects andadvantages and novel features of the present invention may be betterunderstood in light of the following detailed description of a preferredembodiment of the present invention illustrated in the accompanyingdrawing wherein:

FIG. I is a perspective view of a preferred embodi ment of a coreembodying features of the present invention in its unpressurizedcondition;

FIG. 2 is a perspective view of the core of FIG. I in its pressurizedcondition;

FIG. 3 is a sectional view of the core of the present invention takenalong line 3-3 of FIG. 1;

FIG. 4 is a sectional view of one embodiment of a device for making acore embodying features of the present invention;

FIG. 5 is a fragmentary, partially cross-sectional, side view of analternate embodiment of an end portion for the core of FIG. 1; and

FIG. 6 is an end view of the end portion illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing andinitially to FIGS. 1 and 2, there is illustrated a core constructed inaccordance with the principles of the present invention and designatedas a whole by the reference numeral 10. The core 10 is used for formingor casting voids or openings in concrete members, such as concretebeams, slabs and the like, and in general includes a central, hollow,inflatable core body 12 extending between a pair of end portions 14 and16. In one embodiment, the end portions 14 and 16 are formed from asolid, elastomeric material, such as rubber. The end portion 14 includesa longitudinally extending aperture or valve 18 for pressurizing anddepressurizing the body I2. A similar valve may be provided in the endportion 16. A bail or ring 20 may be provided for pulling the core 10from a cast concrete member. The ring 20 may, in the alternateembodiment from that illustrated in FIGS. 1 and 2, be suitably attachedto the end face of the end portion 14 and designed so that itsextremities do not extend beyond the outer periphery of the end portion14 to enable the core to be removed from either end of a void formed ina concrete member.

In use, the core 10 is supported within a form into which concrete ispoured in order to cast a concrete member, such as a concrete beam, slabor the like. The concrete member to be formed may be quite long andextend up to 60 feet or more. Before the concrete is poured, the body 12is pressurized (FIG. 2), as by admitting a pressurized medium such asair to the interior of the body 12 through the valve 18, until the body12 assumes a square, rectangular or other polygonal shape. The body 12is then submerged by the poured concrete and-remains pressurized whilethe concrete sets. When the concrete has set sufficiently to maintainits shape, the pressure in the body 12 is released by opening the valve18 and permitting the pressurizing medium to escape. The core 10 is thenpulled from the concrete member to reveal a square, rectangular or otherpolygonal, longitudinal void.

In accordance with an important feature of the present invention, thebody 12, although extremely simple and inexpensive to construct, iscapable of retaining a generally square, rectangular or other polygonalshape when pressurized without the necessity for any additional support.The ability to form a square, rectangular or other polygonally shapedvoid in a concrete member rather than a circular void enables a savingsin material cost since less concrete is required to form the member ascompared with the amount required to form a member having a circularvoid. Furthermore, as compared with a circular void, the square,rectangular or other polygonally shaped void does not detract from thestrength of the beam. Although the advantages of a square, rectangularor other polygonally shaped void are widely known and appreciated, thepresent invention provides the first feasible, simple, inflatable core10 capable of retaining a square, rectangular or other polygonal shapewhen pressurized without the necessity of the complex supporting andreinforcing structure heretofore required.

In accordance with an important feature of the present invention, thecore body 12 (FIG. 3) includes side walls 12a, corners 12b and a wallportion 22 having an inner sheet 24 of elastomeric material and asimilar outer sheet 26 of elastomeric material. The sheets 24 and 26 areseparated by and reinforced by two layers of fabric 28 and 30. The twolayers 28 and 30 are in turn separated by a central sheet of elastomericmaterial 32. The elastomeric material utilized for the sheets 24, 26 and32 may be butadeiene-styrene rubber, such as GRS rubber, neoprene rubberor any other similar elastomeric material. The hardness of the sheets24, 26 and 32 may be comparable to that normally encountered in atypical conveyor belt construction. The fabric utilized as layers 28 and30 may be polyester, nylon, or polyester and nylon and is preferablywoven into a cloth form to impart strength to the core 10 to enable thecore 10 to be easily removed in a single piece from a void formed in aconcrete member after the concrete has settled.

The core body 12 (FIG. 3) is illustrated in solid line form in itsunpressurized condition and in dotted line form in its pressurizedcondition. For purposes of setting forth a specific operative embodimentof the present invention, a core body 12 for forming a square void of 6inches on each side in a concrete member may have the followingdimensions. The thickness of the wall portion 22 may be approximately5/16 of an inch with the inner and outer sheets 24 and 26 each beingapproximately 3/32 of an inch thick and with the fabric layers 28 and 30and the central sheet 32 comprising the remaining Vs of an inchthickness. In its pressurized form the dimension C" is 6 inches. In itsunpressurized form the dimension A" between the extremities of theadjacent corners 12b or, in other words. between the most greatlyseparated portions of opposite side walls 12a, is approximately 5.125inches. Thus. for this specific embodiment of the present invention theratio of the distance between the most greatly separated portions of theopposite side walls 12a, with the core body 12 in its unpressurizedform, and the distance between the most greatly separated portions ofthe opposite side walls 12a, with the core body 12 in its pressurizedform, (A:C) would be approximately 0.853:I. This ratio (A:C) is notfixed but will vary depending upon the particular construction of thecore body 12 including both the materials used to form the core body 12and the outer dimensions of the core body 12 chosen for a particularembodiment. The dimension B between the most greatly recessed portionsof opposite side walls 12a is approximately 2.675 inches. Thus, for thisspecific embodiment of the present invention in its unpressurized formthe ratio of the greatest distance between opposite side walls 12a tothe smallest distance between opposite side walls 12a (AzB) would beabout 1.92:1. The range of operativeness of a core body 12 in itsunpressurized form constructed in accordance with the principles of thepresent invention is quite wide and includes the ratio range (AzB) ofabout 1.50:1 to 3.00:1.

In accordance with an important feature of the present invention and asclearly illustrated in FIGS. 1 through 3, the sides of the core body 12exhibit a toggle-like action when pressurized wherein the corners 12bare driven radially outwardly as are the side walls 12a so as to assumea square shape having a crosssectional area much greater than thatoccupied by the core body 12 in its unpressurized condition. Thisfeature of the present invention greatly simplifies the removal of thecore 10 from a concrete member.

After the concrete has set sufficiently to retain its shape, the corebody 12 is deflated and returned to its unpressurized condition byopening the valve 18. The core body 12 then returns to its unpressurizedcloverleaf or cross shape due to the tension created in the elastomericside walls 12a. The separation or stripping of the core body 12 from theconcrete initially takes place along radially spaced, longitudinallyextending zones where the tension of the elastomeric side walls 12a isthe greatest, that is, at those portions of the side walls 12a that willreturn to be the most inwardly bowed or recessed portions of the sidewalls 120. As the core body 12 continues to be deflated, the separationfrom the concrete continues from these initial zones in outwardperimetric directions. When completely deflated, the core body 12 willhave completely stripped itself from contact with the inner surfaces ofthe concrete void thus formed and the core 10 may then be easily removedfrom the void in the concrete member.

In accordance with a further important feature of the present invention,a method of making the core 10 of the present invention is illustratedin cross section in FIG. 4. A first step in making the core 10 is toplace the core body 12 over a frame or mandrel 34 formed of foursimilar, longitudinally extending rods 36 held together at their ends bycloverleaf or cross shaped end portions (not shown). The rods 36 mayextend longitudinally for 60 feet or more in order to accommodate corebodies 12 of the same length. The core body 12 initially is extendedover the sides and end of the end portion 16 held in place on the frame34. Subsequently, four similar, longitudinally extending rods 38 aresecured in place on the frame 34 to thereby force the core body 12 intoa cloverleaf or cross shape. The core body 12 is then cured by steam,heat, pressure or by a combination of these processes for several hourson the frame 34. This fuses the elastomeric sheets 24, 26 and 32 (FIG.3) of the core body 12 together and to the end portion 16 and causes thecore body 12 to permanently retain its cloverleaf or cross shape (FIGS.1 and 3) when in its unpressurized condition. After the core body 12 iscured, the rods 38 are removed; and the core body 12 is removed from theframe 34. The other end portion 14 is then secured in an airtightengagement to the core body 12 by conventional fastening means.

Alternately, the core may be placed over a frame or mandrel 34 formed byan integral elongated, hollow member having the desired cross orcloverleaf crosssectional shape. Before curing, the core body 12 may beforced to conform to the cloverleaf or cross shape of such a frame 34 byproviding slots in the elongated, hollow member of the frame 34 and byapplying a vacuum to the hollow interior of the frame 34. Alternately,the exterior of the core body 12 overlying the frame 34 may bepressurized to force the core body 12 into the cloverleaf or cross shapeof the frame 34. The core body 12 is then cured by steam, heat, pressureor by a combination of these processes usually for several hours on theframe 34. After the core body 12 is fully cured, it is removed from theframe 34 and the end portion 14 is secured to the core body 12 asdescribed above.

An alternate embodiment of the end portion 16 is illustrated in FIGS. 5and 6 and is generally designated as 40. The end portion 40 isillustrated as fixed in position on a mandrel or frame 34 during thecuring process. During the curing process, the end portion 40 is fusedto the core body 12.

The end portion 40 includes a plurality of relatively thin, uncuredelastomeric fillers 42 each having the characteristic cloverleaf orcross shape of the core body 12. In a preferred embodiment, theelastomeric fillers 42 may be 3/16 of an inch thick and number 16individual fillers each formed of natural rubber. The fillers 42 aresandwiched between an inner plate 44, having generally the same shape asthe fillers 42 and securely fixed to a hollow, threaded pipe 46, and anoversized backup plate 48. The hollow pipe 46 may, subsequently, beprovided with a valve for admitting or releasing a pressurizing mediumafter the curing process. Furthermore, a bail or ring 20, as describedabove, may be subsequently attached to the outermost end of the hollowpipe 46 to serve as a means for removing the end portion 40 and the corebody 12 from a void formed in a concrete member. In order tocompressively load the fillers 42 during the curing process, a nut 50 isplaced on the threaded end of the pipe 46 to compress the sandwich ofthe inner plate 44, the fillers 42 and the back-up plate 48. A removableconfiguration retainer 52 is used during the curing process to hold thefillers 42 and the inner plate 44 in a precisely aligned relationship.

In accordance with an important feature of the present invention, thetensile strength of the core body 12 is utilized to integrally removethe end portion 40 with the core body 12 from a void formed in aconcrete member after the concrete has sufficiently set so as to retainits shape. The novel use of the tensile strength of the core body 12 tointegrally remove the end portion 40 with the core body 12 is achievedby extending an end portion of the core body 12 beyond and in anoverlapping relationship to the outermost filler 42 in a directionsubstantially transverse to the direction of the longitudinal axis ofthe core body 12. An additional elastomeric filler 54 of the sameconfiguration and. preferably, of the same material as the fillers 42 isplaced between the end portion 120 and the back-up plate 48. The nut 50is then tightened to apply a compressive force to the elements betweenthe inner plate 44 and the back-up plate 48 during the curing process.

After the curing process, the nut 50, the back-up plate 48 and theconfiguration retainer 52 are removed from the end portion 40; and thecore 10, including the core body 12 integrally connected with the endportion 40, may be removed from the frame 34. An end portion for theother end of the core body 12, either similar to the end portion 14 orto the end portion 40, is then securely fastened by any conventionalmeans to the other end of the core body 12. Alternatively, a serratedalu' minum plug, preferably wire bound to the core body 12 and having avalve for admitting or releasing a pressurizing medium, may be used asan end portion for the other end of the core body 12.'The core 10 isthen ready for use in forming polygonal voids in concrete members inaccordance with the principles of the present invention.

Many modifications and variations of the present invention are possiblein light of the above teachings. Thus, it is to be understood that,within the scope of the appended claims, the invention may be practicedotherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A core for use in casting hollow concrete members comprising a first,elongated, inflatable body formed of at least two elastomeric layersseparated by a double layer of reinforcing fabric,

means for sealing the ends of said first body, and

means for admitting a pressurized medium to the interior of said firstbody,

said first body in its unpressurized condition having a substantiallycloverleaf shape of a first crosssectional area and in its pressurizedcondition being capable of maintaining a substantially polygonal shapeof a second cross-sectional area substantially greater than said firstcross-sectional area without the necessity of any additional support.

2. A core as defined in claim 1 wherein at least one of said sealingmeans comprises a second body formed of elastomeric material and havingsaid cloverleaf shape, said second body being integrally connected bycuring to at least an end portion of said first body, said end portionextending in a direction substantially transverse to the direction ofthe longitudinal axis of said first body.

3. A core as defined in claim 1 wherein said polygonal shape comprises asquare shape.

4. A core as defined in claim 1 wherein said cloverleaf shape is formedby said first body having a plurality of corners separated by greatlyrecessed side portions.

5. A core as defined in claim 4 wherein the ratio of the distancebetween the most greatly separated sections of two, opposite ones ofsaid recessed side portions to the distance between the most recessedsections of said two, opposite ones of said recessed side portions is inthe range of from 1.50:1 to 3.00:1.

6. A core as defined in claim 5 wherein said ratio is approximately1.92:1.

7. A core as defined in claim 4 wherein the ratio of the distancebetween the most greatly separated secseparated and reinforced by twofabric means.

1. A core for use in casting hollow concrete members comprising a first,elongated, inflatable body formed of at least two elastomeric layersseparated by a double layer of reinforcing fabric, means for sealing theends of said first body, and means for admitting a pressurized medium tothe interior of said first body, said first body in its unpressurizedcondition having a substantially cloverleaf shape of a firstcross-sectional area and in its pressurized condition being capable ofmaintaining a substantially polygonal shape of a second cross-sectionalarea substantially greater than said first cross-sectional area withoutthe necessity of any additional support.
 2. A core as defined in claim 1wherein at least one of said sealing means comprises a second bodyformed of elastomeric material and having said cloverleaf shape, saidsecond body being integrally connected by curing to at least an endportion of said first body, said end portion extending in a directionsubstantially transverse to the direction of the longitudinal axis ofsaid first body.
 3. A core as defined in claim 1 wherein said polygonalshape comprises a square shape.
 4. A core as defined in claim 1 whereinsaid cloverleaf shape is formed by said first body having a plurality ofcorners separated by greatly recessed side portions.
 5. A core asdefined in claim 4 wherein the ratio of the distance between the mostgreatly separated sections of two, opposite ones of said recessed sideportions to the distance between the most recessed sections of said two,opposite ones of said recessed side portions is in the range of from1.50:1 to 3.00:1.
 6. A core as defined in claim 5 wherein said ratio isapproximately 1.92:1.
 7. A core as defined in claim 4 wherein the ratioof the distance between the most greatly separated sections of twoopposite ones of said recessed side portions of said first body in itsunpressurized condition to the distance between the most greatlyseparated sections of said two, opposite ones of said recessed sideportions of said first body in its pressurized condition isapproximately 0.853:1.
 8. A core as defined in claim 1 wherein saidfirst body comprises an integrally cured sandwich structure includingthree sheets or layers of elastomeric material separated and reinforcedby two fabric means.